High-speed packet data systems rely on carrier-to-interference power ratio (C/I) or signal-to-noise plus interference ratio (SINR) prediction (as is known, C/I and SINR may differ only by a constant factor, and both terms are usually used interchangeably) to efficiently utilize air capacity and reliably deliver the highest speeds possible. If the C/I prediction were not accurate, it would either cause packet delivery errors or waste system resources. For the EV-DO system, the prediction is performed at the mobile station. The mobile station measures channel conditions and predicts the future channel conditions when the expected packet is delivered. For the EV-DV system, the prediction is done at the base station. Here, the mobile station reports C/I measurements to the base station, and the base station predicts the future C/I value for when a scheduled packet is to be transmitted.
The quality of C/I prediction is even more important in systems utilizing phase sweep transmit diversity (PSTD). PSTD was designed to improve temporal diversity by exploiting the spatial diversity of transmit antennas to create faster varying channels. In a PSTD system, the transmit antennas transmit an energy-focused beam across their associated sector at a sweeping frequency. The sweeping frequency imposes additional channel variations on top of the variations induced by movement of mobile stations, and with periodic scanning of the sector, PSTD has the potential to provide fairer channel usage. However, the success of such a system depends on accurately predicting the C/I or SINR.